1. Field of the Invention
The present invention relates to a gas-liquid separator that performs advanced gas-liquid separation such as defoaming or degassing, and is easy to clean or disassemble meeting sanitary specifications.
2. Description of the Prior Art
Generally known systems referred to as gas-liquid separators for defoaming and degassing include container type devices that are filled with liquid and then heated or decompressed, systems that employ a gas permeation membrane where only the gas can pass, and systems employing centrifugation.
Of the above systems, the heating and decompressing types are mainly for batch processing, and are inappropriate for continuous processing, and they have the further disadvantage of larger space requirements. In the permeation membrane type system, clogging of the membrane occurs easily as a result of particles or solids in the liquid, and this entails increased replacement costs.
In contrast, the centrifugation system is appropriate for continuous processing, having the advantage of no impediment from particles and solids. However, since the separation is performed only based on the mass difference between the gas and liquid, the liquid-gas separation performance may be outperformed by the suction power of the vacuum means if an enhanced power vacuum means is installed, which may cause liquid penetration into the vacuum means. Therefore the problem with the centrifugation system is how to achieve strong separation and removal of the gas only.
To solve the aforementioned problem, International Publication WO98/04833 (International Application PCT/JP97/00857 “A self-priming type centrifugal pump”) is an invention which employs safety equipment in the form of a valve mechanism equipped between the pump-type gas-liquid separator and the vacuum means to prevent liquid penetration between the pump and the vacuum means during pump activation, operation, and deactivation. (This invention will be hereinafter called “Original Invention 1”.)
As exemplified in FIG. 16, a main pump 51, a sub-pump 54, and vacuum means 57 are employed in the apparatus according to Original Invention 1; the main pump 51 and the sub-pump 54 are installed across a spacer 53; the central area of a main pump impeller 52 is in communication with a sub-pump suction inlet 54a via the central opening on the spacer 53; a sub-pump discharge outlet 54b is in communication with a main pump suction inlet 51a via a return passage 54c; the central area of a sub-pump impeller 55 is connected to the vacuum means 57 via an exhaust passage 54f. A slow operation valve 58 with delayed opening at pump activation, a quick operation valve 59, which closes immediately when the pump is stopped, and additional protection means (a liquid holding tank) 60 are serially inserted in the exhaust passage 54f. With the adoption of a fluid ring type vacuum pump to the vacuum means 57 in FIG. 16, the slow operation valve 58 opens after a certain period of time has passed due to a gradual increase of the inner pressure in a valve drive chamber 57w in accordance with the fluid pressure increase of the fluid ring type vacuum pump.
Original Invention 1 prevents liquid penetration between the pump and the vacuum means during pump activation, operation, and deactivation, and all operations are performed automatically. Therefore it is extremely practical and useful, however, the following problems still remain unsolved in some applications.
Firstly, there remains the problem of insufficient gas-liquid separation performance when the system is applied to advanced defoaming or degassing operations.
Systems referred to as promoting gas-liquid separation, especially the separation and discharge of dissolved gas in the liquid, include systems employing an orifice in the pumped liquid passage for decompressing or increasing the liquid temperature, however, the problem is how to completely capture the separated gas and separate it from the pumped liquid. For advanced defoaming and degassing performance, enhanced power vacuum means are required, however, this also implies that pumped liquid mixed with gas can be drawn easily into the vacuum means. Furthermore, in the apparatus of Original Invention 1, centrifugal force for gas-liquid separation is generally produced by the main pump impeller 52 rotation, however, because a powerful vortex and turbulent flow are produced at the same time, some gas cannot be separated centrifugally, which may bleed out to a main pump discharge outlet 51b and cause insufficient gas-liquid separation.
Secondly, in applications for treatment of food and ultra-pure liquid, there is the problem of insufficient cleanability, either when the cleaning system is CIP (Cleaning In Place) or COP (Cleaning Out of Place).
Normally, the apparatus used for the above purposes requires, as “sanitary specifications”, not only a flat and smooth wetted surface, but also a structure in which easy CIP (Cleaning In Place: internal cleaning without disassembly), COP (Cleaning Out of Place: disassembled cleaning), and reassembly can be performed. However, the structure of Original Invention 1 is complicated due to multiple impellers 52 and 55, multiple chambers across the spacer 53, and many casing members, which means disassembly is difficult. CIP (Cleaning In Place) of wet areas without leaving any shadows is also difficult due to the complicated passages.
Of the aforementioned problems, International Publication WO01/02732 (International Application PCT/JP00/04508 “Pump apparatus”) is an invention which focuses on solving the first problem, that is, increased gas-liquid separation performance. (This invention will be hereinafter called “Original Invention 2”.)
As exemplified in FIG. 17, the structure of the apparatus according to Original Invention 2 includes a gas-liquid separator installed in the passage of a liquid-feed main pump 71; a gas-liquid separating impeller 73 which rotates by a motor 74 is installed in the gas-liquid separator container 72 provided with an inlet 72a and an outlet 72b; a cavity holder 75 is also installed, which holds the tail bottom of a tornado-shaped cavity s caused by the rotation, preventing it from extending and being suctioned by the main pump 71. Clearance t between the cavity holder 75 and the inner wall of the container 72 is narrowed to allow only the pumped liquid that is pressed against the inner wall of the container 72 by centrifugal force by rotation of the gas-liquid separating impeller 73 to pass through the channel area. An exhaust pipe 76 opens near the center of the tornado-shaped cavity s, to draw out the cavity gas by vacuum means 77 via the exhaust pipe 76 and exhaust passage r.
Also, protection means 78 is installed to the exhaust passage r which only passes the gas to the vacuum means 77, preventing the pumped liquid from passing if the pumped liquid is mixed into the exhaust gas. In addition, a gas return passage u and a boosting means 79 are also employed for special usage in remixing the exhausted gas into the pumped liquid after the liquid is sent by the main pump 71, returning the pumped liquid to its original condition.
In Original Invention 2, gas bubbles in the pumped liquid are forcibly separated by centrifugal force by the rotation of the gas-liquid separating impeller 73, apart from the main pump 71 impeller, and the cavity holder 75 prevents the tail bottom of the tornado-shaped cavity s from extending and passing through the main pump 71 side. Furthermore, since the rotating liquid pushed against the inner wall of the container 72 flows through clearance t by priority, there is little possibility of gas bubbles passing through from clearance t. Therefore, gas can be gathered effectively and drawn out by the vacuum means 77. Due to this, the aforementioned first problem, that is the gas-liquid separation performance, has been largely resolved.
For Original Invention 2, however, the aforementioned second problem, that is the insufficient cleanability of the system, has not been resolved in any way. There is, instead, renewed occurrence of shadows or bottlenecks which create cleaning problems such as on the back side of the cavity holder 75 or in the exhaust pipe 76 installation part due to the cavity holder 75 or clearance t employed to improve the gas-liquid separation performance. The system is not applicable to various kinds of liquids because there is the possibility of clogging due to the bottleneck if particles or masses are mixed in the liquid such as food material. And, furthermore, if the formed cavity becomes unstable, the mixing of pumped liquid cannot be prevented in the gas-liquid separator because the cavity is simply drawn into the exhaust pipe 76 opening, and therefore, subsequent problems such as the elimination of the mixed liquid require the separate installation of the protection means 78.
These problems are caused inevitably due to the structure of Original Invention 2, and from a technical perspective pose difficulty in solving. Foremost, if gas-liquid separation performance improvement is the main focus, the structural composition becomes complicated, with the trade-off being insufficient cleanability. Therefore, resolving the aforementioned two problems, that is “gas-liquid separation performance” and “ease of cleaning” at the same time seemed a difficult challenge.
An object of the present invention, in respect to the previously mentioned circumstances, is to provide a gas-liquid separator with enhanced performance and easy operation in a simple gas-liquid separation mechanism with safe and assured operation, enabling application of powerful vacuum means to perform gas-liquid separation such as advanced defoaming or degassing, facilitating easy cleaning with CIP (Cleaning In Place) and COP (Cleaning Out of Place) ability that meets sanitary specifications, and enabling application to various kinds of liquids.